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main.c
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main.c
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#include <assert.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "riscv-opcodes/encoding.out.h"
#define MEMORY_SIZE 0x10000000
#define UART_ADDR 0x200
#define START_ADDRESS 0x1000
struct __attribute__((__packed__)) insn_r {
unsigned opcode : 7;
unsigned rd : 5;
unsigned funct3 : 3;
unsigned rs1 : 5;
unsigned rs2 : 5;
unsigned funct7 : 7;
};
struct __attribute__((__packed__)) insn_i {
unsigned opcode : 7;
unsigned rd : 5;
unsigned funct3 : 3;
unsigned rs1 : 5;
int imm : 12;
};
struct __attribute__((__packed__)) insn_s {
unsigned opcode : 7;
unsigned imm_low : 5;
unsigned funct3 : 3;
unsigned rs1 : 5;
unsigned rs2 : 5;
int imm_high : 7;
};
struct __attribute__((__packed__)) insn_u {
unsigned opcode : 7;
unsigned rd : 5;
int imm : 20;
};
static_assert(sizeof(struct insn_r) == 4, "struct insn_r is incorrect size");
static_assert(sizeof(struct insn_i) == 4, "struct insn_i is incorrect size");
static_assert(sizeof(struct insn_s) == 4, "struct insn_i is incorrect size");
static_assert(sizeof(struct insn_u) == 4, "struct insn_i is incorrect size");
// Ensure distinction between logical and arithmetic shift
static_assert((-5 >> 1) == -3, "arithmetic right shift is not correct");
static_assert(((unsigned)-5 >> 1) == 0x7FFFFFFD,
"logical right shift is not correct");
static_assert((-1 & 3) == 3, "compiler does not use two's complement");
int insn_s_get_imm(struct insn_s insn) {
return (insn.imm_high << 5) + insn.imm_low;
}
// Linux needs S abd Zicsr
int main(int argc, char **argv) {
uint32_t pc = START_ADDRESS;
uint32_t __attribute__((aligned(4))) x[32] = {0};
char *memory = malloc(sizeof(char) * MEMORY_SIZE);
assert(memory);
size_t ret;
FILE *code_file;
if (argc != 2) {
fputs("Incorrect number of arguments.\n", stderr);
return EXIT_FAILURE;
}
code_file = fopen(argv[1], "rb");
if (!code_file) {
perror("fopen");
return EXIT_FAILURE;
}
ret = fread(memory + START_ADDRESS, sizeof(*memory),
MEMORY_SIZE - START_ADDRESS, code_file);
if (!ret) {
perror("fread");
return EXIT_FAILURE;
}
uint32_t current_instruction;
uint32_t store_offset;
for (current_instruction = *(uint32_t *)(memory + pc); 1;
current_instruction = *(uint32_t *)(memory + pc)) {
// printf("PC: %lx, INSN: %x\n", pc, current_instruction);
store_offset = 0;
// I type
if ((current_instruction & MASK_ADDI) == MATCH_ADDI) {
struct insn_i insn = *(struct insn_i *)¤t_instruction;
if (insn.rd)
x[insn.rd] = x[insn.rs1] + insn.imm;
} else if ((current_instruction & MASK_SLTI) == MATCH_SLTI) {
struct insn_i insn = *(struct insn_i *)¤t_instruction;
if (insn.rd)
x[insn.rd] = (int32_t)x[insn.rs1] < insn.imm;
} else if ((current_instruction & MASK_SLTIU) == MATCH_SLTIU) {
struct insn_i insn = *(struct insn_i *)¤t_instruction;
if (insn.rd)
x[insn.rd] = x[insn.rs1] < (uint32_t)insn.imm;
} else if ((current_instruction & MASK_ANDI) == MATCH_ANDI) {
struct insn_i insn = *(struct insn_i *)¤t_instruction;
if (insn.rd)
x[insn.rd] = x[insn.rs1] & insn.imm;
} else if ((current_instruction & MASK_ORI) == MATCH_ORI) {
struct insn_i insn = *(struct insn_i *)¤t_instruction;
if (insn.rd)
x[insn.rd] = x[insn.rs1] | insn.imm;
} else if ((current_instruction & MASK_XORI) == MATCH_XORI) {
struct insn_i insn = *(struct insn_i *)¤t_instruction;
if (insn.rd)
x[insn.rd] = x[insn.rs1] ^ insn.imm;
}
// TODO: "the sign bit for all immediates is always held in bit 31 of the
// instruction"
else if ((current_instruction & MASK_SLLI) == MATCH_SLLI) {
struct insn_i insn = *(struct insn_i *)¤t_instruction;
if (insn.rd)
x[insn.rd] = x[insn.rs1]
<< ((unsigned)insn.imm & 0b11111); // 0b111111 if rv64
} else if ((current_instruction & MASK_SRLI) == MATCH_SRLI) {
struct insn_i insn = *(struct insn_i *)¤t_instruction;
if (insn.rd)
x[insn.rd] = x[insn.rs1] >> ((unsigned)insn.imm & 0b11111);
} else if ((current_instruction & MASK_SRAI) == MATCH_SRAI) {
struct insn_i insn = *(struct insn_i *)¤t_instruction;
// TODO: this is probably too many casts but better safe than sorry
if (insn.rd)
x[insn.rd] =
(int32_t)x[insn.rs1] >> (int)((unsigned)insn.imm & 0b11111);
}
// U type (should U-immediate get be a function?)
else if ((current_instruction & MASK_LUI) == MATCH_LUI) {
struct insn_u insn = *(struct insn_u *)¤t_instruction;
if (insn.rd)
x[insn.rd] = insn.imm << 12;
} else if ((current_instruction & MASK_LUI) == MATCH_LUI) {
struct insn_u insn = *(struct insn_u *)¤t_instruction;
if (insn.rd)
x[insn.rd] = pc + (insn.imm << 12);
}
// R type - reg to reg
else if ((current_instruction & MASK_ADD) == MATCH_ADD) {
struct insn_r insn = *(struct insn_r *)¤t_instruction;
x[insn.rd] = x[insn.rs1] + x[insn.rs2];
} else if ((current_instruction & MASK_SLT) == MATCH_SLT) {
struct insn_r insn = *(struct insn_r *)¤t_instruction;
x[insn.rd] = (int32_t)x[insn.rs1] < (int32_t)x[insn.rs2];
} else if ((current_instruction & MASK_SLTU) == MATCH_SLTU) {
struct insn_r insn = *(struct insn_r *)¤t_instruction;
x[insn.rd] = x[insn.rs1] < x[insn.rs2];
} else if ((current_instruction & MASK_AND) == MATCH_AND) {
struct insn_r insn = *(struct insn_r *)¤t_instruction;
x[insn.rd] = x[insn.rs1] & x[insn.rs2];
} else if ((current_instruction & MASK_OR) == MATCH_OR) {
struct insn_r insn = *(struct insn_r *)¤t_instruction;
x[insn.rd] = x[insn.rs1] | x[insn.rs2];
} else if ((current_instruction & MASK_XOR) == MATCH_XOR) {
struct insn_r insn = *(struct insn_r *)¤t_instruction;
x[insn.rd] = x[insn.rs1] ^ x[insn.rs2];
} else if ((current_instruction & MASK_SLL) == MATCH_SLL) {
struct insn_r insn = *(struct insn_r *)¤t_instruction;
x[insn.rd] = x[insn.rs1] << (x[insn.rs2] & 0b11111);
} else if ((current_instruction & MASK_SRL) == MATCH_SRL) {
struct insn_r insn = *(struct insn_r *)¤t_instruction;
x[insn.rd] = x[insn.rs1] << (x[insn.rs2] & 0b11111);
} else if ((current_instruction & MASK_SRA) == MATCH_SRA) {
struct insn_r insn = *(struct insn_r *)¤t_instruction;
x[insn.rd] = (int32_t)x[insn.rs1] << (int32_t)(x[insn.rs2] & 0b11111);
} else if ((current_instruction & MASK_SUB) == MATCH_SUB) {
struct insn_r insn = *(struct insn_r *)¤t_instruction;
x[insn.rd] = x[insn.rs1] - x[insn.rs2];
}
// Jump goes here
// Load
else if ((current_instruction & MASK_LW) == MATCH_LW) {
struct insn_i insn = *(struct insn_i *)¤t_instruction;
x[insn.rd] = *(int32_t *)(memory + x[insn.rs1] + insn.imm);
} else if ((current_instruction & MASK_LH) == MATCH_LH) {
struct insn_i insn = *(struct insn_i *)¤t_instruction;
x[insn.rd] = *(int16_t *)(memory + x[insn.rs1] + insn.imm);
} else if ((current_instruction & MASK_LHU) == MATCH_LHU) {
struct insn_i insn = *(struct insn_i *)¤t_instruction;
x[insn.rd] = *(uint16_t *)(memory + x[insn.rs1] + insn.imm);
} else if ((current_instruction & MASK_LB) == MATCH_LB) {
struct insn_i insn = *(struct insn_i *)¤t_instruction;
x[insn.rd] = *(int8_t *)(memory + x[insn.rs1] + insn.imm);
} else if ((current_instruction & MASK_LBU) == MATCH_LBU) {
struct insn_i insn = *(struct insn_i *)¤t_instruction;
x[insn.rd] = *(uint8_t *)(memory + x[insn.rs1] + insn.imm);
}
// Store
else if ((current_instruction & MASK_SW) == MATCH_SW) {
struct insn_s insn = *(struct insn_s *)¤t_instruction;
store_offset = x[insn.rs1] + insn_s_get_imm(insn);
memcpy(memory + store_offset, &x[insn.rs2], 4);
} else if ((current_instruction & MASK_SH) == MATCH_SH) {
struct insn_s insn = *(struct insn_s *)¤t_instruction;
store_offset = x[insn.rs1] + insn_s_get_imm(insn);
memcpy(memory + store_offset, &x[insn.rs2], 2);
} else if ((current_instruction & MASK_SB) == MATCH_SB) {
struct insn_s insn = *(struct insn_s *)¤t_instruction;
store_offset = x[insn.rs1] + insn_s_get_imm(insn);
memcpy(memory + store_offset, &x[insn.rs2], 1);
} else {
fputs("Illegal instruction!\n", stderr);
return EXIT_FAILURE;
}
if (store_offset == UART_ADDR) {
putchar(memory[UART_ADDR]);
}
x[0] = 0;
if (pc == 0x1048)
break;
pc += 4;
}
}